1. Field of the Invention
The invention is generally related to the field of heat transfer. More specifically, the invention relates to recovery of hydrogen or helium in systems using hydrogen or helium as a heat transfer fluid, in conjunction with a second gas, where air contaminants may be problematic.
2. Related Art
Pure or relatively pure hydrogen and helium have excellent heat transfer properties. For example, helium is typically employed to enhance fiber cooling during the optical fiber drawing process because it is chemically inert and because of its heat transfer properties. Of the common pure gases, only hydrogen has a higher thermal conductivity than pure helium.
For example, in optical fiber manufacturing, helium is currently the preferred heat transfer fluid, although other gases have been used, such as hydrogen, argon, nitrogen, even oxygen. Helium, alone or in mixtures, is used during perform lay down, consolidation, in the fiber drawing furnace, and in drawn fiber cooling prior to the application of resin coatings. See for example the following United States patents and other references:
U.S. Pat. No. 4,126,436 (oxygen plus nitrogen); U.S. Pat. No. 4,154,592 (increased addition of helium to mixtures of oxygen and nitrogen produce lower variation in fiber diameter); U.S. Pat. No. 4,400,190 (use of argon as a xe2x80x9cgas curtainxe2x80x9d); U.S. Pat. No. 4,437,870 (cool dry helium flowed from a porous tube or an annular slot surrounding the fiber); U.S. Pat. No. 4,664,689 (helium, nitrogen, argon, or hydrogen); U.S. Pat. No. 4,673,427 (argon, oxygen, or nitrogen); U.S. Pat. No. 4,761,168 (air, helium, or nitrogen); U.S. Pat. No. 4,838,918 (gaseous nitrogen at room temperature, with liquid nitrogen flowing in hollow parallel plates to cool the gaseous nitrogen); U.S. Pat. No. 4,913,715 (helium and/or hydrogen); U.S. Pat. No. 4,988,374 (use of a removable insert to prevent SiO2 from depositing on the hot fiber); U.S. Pat. No. 5,059,229 (helium/hydrogen mixtures, or hydrogen plus argon, helium, oxygen, nitrogen, and/or air); U.S. Pat. No. 5,160,359 (use of helium, co-currently, with rotation); U.S. Pat. No. 5,284,499 (helium or argon); U.S. Pat. No. 5,377,491 (at least one of helium, nitrogen, hydrogen, carbon dioxide); U.S. Pat. No. 5,897,682 (helium, or helium plus a non-combustible amount of hydrogen, or helium plus nitrogen or argon); U.S. Pat. No. 6,092,391 (use of helium of various purities, depending on unit operation); JP 62-246837 (use of inert gas flowing in a tube such that temperature differential between the inert gas and air is small, supposedly reducing ambient air ingress); EP 321,182 (use of a tubular recovery chamber, and seal between draw furnace and recovery chamber to prevent air ingress into chamber).
Many of the systems discussed in these patent documents are engineering marvels but, unfortunately, are incredibly expensive from an equipment standpoint, and/or are space intensive in their efforts to reduce or eliminate air from the system. This also eliminates nitrogen, which can have beneficial heat transfer aspects. It would be advantageous if apparatus and methods could be developed to take advantage of the heat transfer properties of helium and hydrogen, while reducing the ingress of contaminants into many manufacturing processes. It would be a further advantage in the heat transfer art to efficiently recycle at least a portion of the hydrogen or helium, without using high-pressure equipment and its attendant cost and space requirements.
In accordance with the present invention, methods and apparatus are presented which reduce or overcome shortcomings in the known methods and apparatus, in particular, where contamination is problematic. Hydrogen and helium are employed as the heat transfer fluids in a heat exchange unit, and a seal gas selected from the group consisting of argon, carbon dioxide, and nitrogen is used as a seal gas. The seal gas and the heat transfer fluid exit the heat transfer unit together, in a mixed or unmixed state. As used herein xe2x80x9ccontaminantxe2x80x9d includes, but is not limited to oxygen, moisture, hydrocarbons such as alkanes, alkenes, alkynes, alcohols, halogenated hydrocarbons, including perfluorinated compounds such as tetrafluoromethane and hexafluoroethane, and the like, but excludes nitrogen, carbon dioxide, and argon. When contaminant is defined in this way, certain advantages may be realized in operating recycle equipment for the combination of gases exiting the heat exchange unit.
A first aspect of the invention is a method of cooling an object, the method comprising:
a) contacting the object with a heat transfer fluid comprising a major component selected from the group consisting of hydrogen and helium, the object traversing through a heat exchange unit having an object inlet end and an object outlet end;
b) preventing ingress of contaminants into the heat exchange unit inlet end and outlet end using a seal gas comprising a major component selected from the group consisting of argon, carbon dioxide, and nitrogen, the seal gas exiting with the heat transfer fluid to form an exit gas (either mixed or not);
c) compressing the exit gas to form a compressed recycle gas;
d) routing the compressed recycle gas to a condenser where the compressed recycle gas is cooled to form a cooled recycle composition, and routing the cooled recycle composition to a gas-liquid separator, thus forming an enriched gas that functions as the heat transfer fluid, and an enriched liquid, preferably that when vaporized functions as the seal gas; and
e) preferably heating the enriched liquid to form the seal gas.
The seal gas is preferably receycled, but is not required to be. In other, words, fresh seal gas may be employed. In any event, at least a portion of the heat transfer fluid is recycled.
A second aspect of the invention is a method of cooling an object, the method comprising:
a) contacting the object with a heat transfer fluid comprising a major component selected from the group consisting of hydrogen and helium, the object traversing through a heat exchange unit having an object inlet end and an object outlet end;
b) preventing ingress of contaminants into the heat exchange unit inlet end and outlet end using a seal gas comprising a major component selected from the group consisting of argon, carbon dioxide, and nitrogen, the seal gas exiting with the heat transfer fluid to form an exit gas;
c) compressing the exit gas to form a compressed recycle gas;
d) routing the compressed recycle gas to a recycle gas heat exchanger, where the compressed recycle gas exchanges heat with an enriched liquid to form a mixture comprising the seal gas, and a chilled compressed recycle gas;
e) routing the chilled compressed recycle gas to a condenser where the chilled compressed recycle gas is cooled to form a cooled recycle composition, and routing the cooled recycle composition to a gas-liquid separator, thus forming an enriched gas which functions as the heat transfer fluid, and the enriched liquid; and
f) preferably routing the enriched liquid to the recycle gas heat exchanger and thus forming the seal gas.
A third aspect of the invention is a method of cooling an object, the method comprising:
a) contacting the object with a heat transfer fluid comprising a major component selected from the group consisting of hydrogen and helium, the object traversing through a heat exchange unit having an object inlet end and an object outlet end;
b) preventing ingress of contaminants into the heat exchange unit inlet end and outlet end using a seal gas comprising a major component selected from the group consisting of argon, carbon dioxide, and nitrogen, the seal gas exiting with the heat transfer fluid to form an exit gas;
c) compressing the exit gas to form a compressed recycle gas;
d) routing the compressed recycle gas to a recuperator, where the compressed recycle gas exchanges heat with an enriched liquid to form a composition comprising the seal gas and a chilled compressed recycle gas, and wherein the compressed recycle gas also exchanges heat with an enriched gas;
e) routing the chilled compressed recycle gas to a condenser where the chilled compressed recycle gas is cooled to form a cooled recycle composition, and routing the cooled recycle composition to a gas-liquid separator, thus forming the enriched gas and the enriched liquid; and
f) routing the enriched gas, and preferably the enriched liquid, to the recuperator.
As used herein the term xe2x80x9cobjectxe2x80x9d includes, but is not limited to, optical fiber performs, electrical parts such as circuit boards, sub-assemblies, and integrated circuits, metals parts, ceramic parts, and the like. Also, as used herein the term xe2x80x9cheat exchange unitxe2x80x9d means any apparatus that allows objects to enter and leave a space, either continuously, semi-continuously, or batch-wise, and includes, but is not limited to optical fiber cooling heat exchangers, wave soldering machines, reflow soldering machines, cold treating units, environmental testing cabinets, and the like. It will be understood that in certain preferred embodiments, the object inlet end and object outlet end may be one and the same, as for example in heat exchange units that have a door or xe2x80x9cload-lockxe2x80x9d apparatus for insertion and removal of objects.
Preferred are methods in accordance with each method aspect of the invention wherein either the temperature, the pressure, or both temperature and pressure of the cooled compressed recycle gas exiting the condenser is controlled to ensure that heat transfer demand in the heat exchange unit is met at the lowest possible pressure, to reduce cost of compression equipment and utilities.
A fourth aspect of the invention is an apparatus comprising:
a) a heat exchange unit for cooling an object having an object inlet end and an object outlet end, and means for allowing a heat transfer fluid selected from the group consisting of hydrogen and helium to contact the object, the heat exchange unit adapted to have the object traverse there through in a mode selected from the group consisting of continuous mode, semi-continuous mode, or batch mode;
b) means for preventing ingress of contaminants into the heat exchange unit object inlet end and object outlet end, the means for preventing ingress of contaminants adapted to use a seal gas selected form the group consisting of argon, carbon dioxide, and nitrogen, the means for preventing ingress of contaminants allowing the seal gas to exit the heat exchange unit with the heat transfer fluid to form an exit gas;
c) means for compressing the exit gas to form a compressed recycle gas;
d) means for routing the compressed recycle gas to a condenser where the compressed recycle gas is cooled to form a cooled recycle composition, and means for routing the cooled recycle composition to a gas-liquid separator, thus forming an enriched gas that functions as the heat transfer fluid, and an enriched liquid; and
e) preferably means for heating the enriched liquid to form the seal gas.
A fifth embodiment of the invention is an apparatus comprising:
a) a heat exchange unit for cooling an object having an object inlet end and an object outlet end, and means for allowing a heat transfer fluid selected from the group consisting of hydrogen and helium to contact the object, the heat exchange unit adapted to have the object traverse there through in a mode selected from the group consisting of continuous mode, semi-continuous mode, or batch mode;
b) means for preventing ingress of contaminants into the heat exchange unit object inlet end and object outlet end, the means for preventing ingress of contaminants adapted to use a seal gas comprising a major component selected from the group consisting of argon, carbon dioxide, and nitrogen, the means for preventing ingress of contaminants allowing the seal gas to exit with the heat transfer fluid to form an exit gas;
c) means for compressing the exit gas to form a compressed recycle gas;
d) means for routing the compressed recycled gas to a recycle gas heat exchanger allowing exchange of heat between the compressed recycle gas and an enriched liquid, thus adapted to form a chilled compressed recycle gas and a composition comprising the seal gas;
e) means for routing the chilled compressed recycle gas to a condenser where the chilled compressed recycle gas is cooled to form a cooled recycle composition, and means for routing the cooled recycle composition to a gas-liquid separator, thus forming an enriched gas which functions as the heat transfer fluid, and forming the enriched liquid; and
f) preferably means for routing the enriched liquid to the recycle gas heat exchanger and thus forming the seal gas.
A sixth aspect of the invention is an apparatus comprising:
a) a heat exchange unit for cooling an object having an object inlet end and an object outlet end, and means for allowing a heat transfer fluid selected from the group consisting of hydrogen and helium to contact the object, the heat exchange unit adapted to have the object traverse there through in a mode selected from the group consisting of continuous mode, semi-continuous mode, or batch mode;
b) means for preventing ingress of contaminants into the heat exchange unit object inlet end and object outlet end, the means for preventing ingress of contaminants adapted to use a seal gas selected from the group consisting of argon, carbon dioxide, and nitrogen as a major component, the means for preventing ingress of contaminants allowing seal gas to exit with the heat transfer fluid to form an exit gas;
c) means for compressing the exit gas to form a compressed recycle gas;
d) means for routing the compressed recycle gas to a recuperator, where the compressed recycle gas exchanges heat with an enriched liquid to form a composition comprising the seal gas and a chilled compressed recycle composition, and wherein the compressed recycle gas also exchanges heat with an enriched gas;
e) means for routing the chilled compressed recycle composition to a condenser where the chilled compressed recycle composition is cooled to form a cooled recycle composition, and routing the cooled recycle composition to a gas-liquid separator, thus forming the enriched gas and the enriched liquid; and
f) preferably means for routing the enriched liquid and the enriched gas to the recuperator.
Further aspects and advantages of the invention will become apparent by reviewing the description of preferred embodiments that follows.